Questions related to the perception and measurement of light (primarily in the visible range), its mathematical description, the reproduction of colors by different means, color combinations, etc. Please use the tag [electromagnetic-radiation] if you want to refer to the general form of light.
3
votes
1answer
122 views
Was the choice of red/green colors for traffic lights a happy coincidence?
All of us have learned since secondary school that the reason we use red in the traffic lights for "Stop" is because it travels the furthest without dispersion. According to wikipedia which cites ...
3
votes
3answers
171 views
Why does it require such little energy to create the fastest thing in the universe?
I have noticed when I turn on the light switch in my house light comes from the bulb.
How is this light created?(process occurring in the bulb) and why is this small amount of electricity enough to ...
2
votes
5answers
2k views
Focal Point vs where you see the images
I am trying to figure out where is the focal point and where is the image. I read some information online about the point where you see the image is the focal point, but however, my supervisor ...
1
vote
1answer
50 views
How large of a solar sail would be needed to travel to mars in under a year?
I'm attempting to approach this using the identity
$$F/A = I/c$$
I can solve for Area easily enough
$$A = F(c/I)$$
and I know the distance $d$ is
$$d=1/2(at^2)$$
But I'm having difficulty trying to ...
-1
votes
3answers
166 views
Does the Lorentz transformation not apply to light?
Since you would know that light always travels at the constant velocity with respect to all frame of reference ....according to relativity whenever we are traveling at speed of light our time with ...
10
votes
5answers
105 views
How large is the universe?
We know that the age of the universe (or, at least the time since the Big Bang) is roughly 13.75 billion years. I have heard that the size of the universe is much larger than what we can see, in other ...
9
votes
5answers
509 views
Superposition of electromagnetic waves
The superposition of two waves is given by
$$\sin(\omega_1 t)+\sin(\omega_2 t)=2\cos\left(\frac{\omega_1-\omega_2}{2}t\right)\sin\left(\frac{\omega_1+\omega_2}{2}t\right).$$
For sound waves, this ...
7
votes
2answers
446 views
What does the sky look like to human eyes from orbit?
There are numerous pictures, obviously, of the blackness of space from the shuttle, the space station, and even the moon. But they all suffer from being from the perspective of a camera, which is not ...
6
votes
2answers
325 views
What is changing in latest light bulb technologies?
I'm confused with the latest home lightning bulbs.
Understanding filament bulbs was easy. For example take 220V, 100W filament bulb:
Power = $V^2/R$ Filament gets heated and emits energy in the form ...
4
votes
2answers
160 views
Can a dot of light travel faster than the speed of light? [duplicate]
Say I have a laser. If I spin the laser so that the beam sweeps in an arc along a very distant object, could that dot travel faster than the speed of light?
In Diagram form:
4
votes
2answers
182 views
How photons represent colors that you see?
Right now, my understanding is that, a mixture of photons of many different frequencies is perceived as white by your eye. While no photons at all, is perceived as black. And photons with the blue ...
3
votes
10answers
600 views
Why do we think of light as a wave?
I've read that light travels in a straight line and has a wavelength of 400nm to 700nm. But I don't understand why does it have a wavelength and what creates its wavelength? I agree with the concept ...
3
votes
1answer
806 views
Purple doesn't occur in rainbow - or does it?
Usually, when asked whether the purple color exists rainbows, an answer similar to this is given:
The purple color is perceived by human eyes via the activation of both red-sensitive and ...
3
votes
1answer
401 views
Formula for polarized “light” transmission through close filters?
I'm still trying to understand photons (or polarized electromagnetic radiation).
This question is similar to one of my previous questions, but different:
Consider the famous demonstration of crossed ...
3
votes
2answers
2k views
What invisible flicker do different types of light bulbs have?
What waveform does the light coming off different types of artificial light sources have and (of course) what are the underlying physical reason for them?
I was inspired to ask this question ...
2
votes
1answer
264 views
Gravitational Redshift around a Schwarzschild Black Hole
Let's say that I'm hovering in a rocket at constant spatial coordinates outside a Schwarzschild black hole.
I drop a bulb into the black hole, and it emits some light at a distance of $r_e$ from the ...
2
votes
2answers
340 views
Electron model under Maxwell's theory
I was not able to recall my memories, so:
What is the formula that states the frequency of electrons revolving around nucleus is equal to the frequency of light (or photon) emitted (or radiated)?
(I ...
2
votes
1answer
461 views
Visible light spectrum to color space
I need to be able to convert an arbitrary emission spectrum in the visible spectrum range (i.e. for every wavelength between 380 and 780, I have a number between 0 and 1 that represents the ...
2
votes
4answers
1k views
Is it only red, green and blue that can make up any color through additive mixture?
I'm reading about color vision and have some trouble understanding the motivation for why the trichromatic theory was suggested in the first place. The book I'm reading ("Psychgology: The science of ...
2
votes
1answer
320 views
Snell's Law of Refraction
I was told that "Snell's law of refraction implies that a light ray in an isotropic medium travels from point a to point b in stationary time." Why is this true?
Thanks.
2
votes
1answer
504 views
Effects of high frequency lighting on human vision?
I have a couple of different LED flashlights. One of them has three different "modes" of brightness, and the way it controls it is via pulse width modulation (PWM). Here is a picture that illustrates ...
1
vote
4answers
210 views
Light traveling through a medium
Does the frequency of light change when it travels across an interface between two media? What happens to the light wavelength and the light velocity at the interface?
I've gotten different answers ...
1
vote
2answers
1k views
Why can't light pass through walls but sound can?
when i sit in a room....i can hear voices coming from the adjacent room but the light in adjacent room does not enter my room i.e. sound waves travels through the wall but light waves can't.why?
1
vote
2answers
428 views
Reflectance vs. Thin Metal film Thickness Graph
Is there formula that gives reflectance of very thin film of given metal (tens of nanometers) to the visible light of given wavelength(808nm) ? Which properties of metals are needed for the formula ?
...
1
vote
1answer
141 views
How does a strobe lamp stop a fast moving object?
A strobe lamp can be used to seemingly stop a fast moving object when calibrated.
Commonly used in quality assurance during production to inspect otherwise non-observable assembly line activity.
What ...
1
vote
1answer
104 views
Why does separating plastic from a cough drop create flashes?
I was tearing open individually-wrapped cough drops in the dark, and noticed that when I pulled apart two adhesive-joined pieces of silvery plastic film, small flashes of light were produced. It was ...
1
vote
3answers
457 views
Conversion formula from spectrophotometer readings to any standard color space profile?
I have readings of colors from a spectrophotometer that records across the human visible color spectrum 390nm to 790nm intervals. I'd like to convert this into any color space, could be CIE XYZ, HSL, ...
0
votes
1answer
40 views
How does gravity effects both time and light if they have no mass [duplicate]
I've been reading about how black holes can effect both time and light with gravity. So I was wondering, doesn't something have to have mass to be effected by gravity? And if so, does this mean both ...
0
votes
1answer
42 views
Is there a way to see light frequencies invisible to the human eye without the use of electronic sensors?
I wonder if it's possible to be able to see light frequencies that cannot be normally seen by human eye, without using sensors designed specifically for detecting a certain spectrum range, but rather ...
0
votes
1answer
155 views
Transmission of Gaussian Beam Through Graded-Index Slab
The $ABCD$ matrix of a glass graded-index slab with refractive index $n(y)=n_0(1-\frac{1}{2}\alpha^{2}y^{2})$ and length $d$ is $A=\cos(\alpha d)$, $B=\frac{1}{\alpha}\sin(\alpha d)$, $C=-\alpha ...
